68Ga-FAPI-04 PET/MR is helpful in differential diagnosis of pancreatitis from pancreatic malignancy compared to 18F-FDG PET/CT: a case report.

Introduction: ⁶⁸Ga-fibroblast activation protein-specific enzyme inhibitor 04 (FAPI-04) is a radiolabelled molecular agent targeting the inhibitor of fibroblast activation protein (FAP), which is often present in tumor stroma and inflammatory tissue with prominent fibroblast proliferation. FAPI-04 is a promising PET tracer for tumor imaging as well as IgG4-related disease (IgG4-RD).

Case description: We herein present a case where ⁶⁸Ga-FAPI PET/MR helped to diagnose IgG4-RD that involved pancreas and bile duct. A 62-year-old patient suffered from diffusive discomfort at middle upper abdomen and presented brown urine. Blood test revealed abnormal liver function and elevated IgG4 (4.830g/L↑). ¹⁸F-FDG PET showed enlarged uncinate process and dilated bile duct tree. Mild increase of FDG uptake in uncinate process and head of pancreas indicated possible pancreatic malignancy, but the clinical evidence was not sufficient and histology examination was negative. ⁶⁸Ga-FAPI PET revealed prominent increased radioactivity distribution in the entire pancreas and bile duct, suggesting IgG4-RD.

Conclusion: FAPI-04 is not only a good PET imaging tracer for tumors, but also for prominent fibroblast-mediated inflammation. FAPI imaging should be considered when the diagnosis using ¹⁸F-FDG imaging is ambiguous. The presented case illustrates that ⁶⁸Ga-FAPI-04 PET is helpful in improving the differential diagnosis of pancreatitis and pancreatic cancer.